Nanoparticle superlattices represent a new class of advanced metamaterials which have exhibited unusual optical, electrical, plasmonic, magnetic and mechanical properties. In particular, two-dimensional (2D) ordered plasmonic nanoparticle arrays can take full advantage of the shape-dependence, spatial arrangement, and directional properties of the nanoparticle. The properties of these superlattice sheets can be adjusted by controlling the nanoparticle size and adjusting the interparticle spacing, changing the shape of the constituent nanoparticles and further tuning their orientations. In principle, any plasmonic particles in the “artificial nanoparticle periodic table” could be used as constituent elements towards the fabrication of superlattice solids. However, only a few plasmonic nanoparticles have been successfully utilized in nanosheets fabrication due to the extreme difficulties in controlled self-assembly, limiting the further application of 2D superlattice.<br/>Here, by using a new plasmonic element – gold nanobipyramid (Au NBP) as building blocks, we fabricated a new type of plasmonic nanoparticle superlattice, which showed four distinct orientational packing orders, corresponding to horizontal alignment, circular arrangement, slanted alignment and vertical alignment of constituent particle building elements. The orientational packing ordering directly influenced plasmonic coupling strength and modes, hence, determined the surface-enhanced Raman scattering (SERS) enhancements of plasmonic superlattices. In particular, vertical alignment structures showed the highest Raman enhancement factor, which was about 77-fold greater than the horizontal alignment arrays and about 19-fold greater than circular arrangement. The results reveal the nature and significance of orientational ordering in controlling plasmonic coupling and SERS enhancements of ordered plasmonic nanoparticle arrays.

Two-dimensional bipyramid plasmonic nanoparticle superstructure with four distinct orientational packing orders

253rd National Meeting (2017)

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